With the video and audio multimedia technologies and Internet applications thriving tremendously, performances of hardware equipment (such as hard disk drives, card readers, optical disk burners, etc.) of personal computers and servers also are enhanced. However, the original power supply device usually aims to provide a fixed power capacity. In the event that the added new hardware equipment exceed the power capacity of the power supply device, users have to purchase a more powerful power supply device to provide enough electric power to meet operation requirement. For power supply device manufacturers, to fabricate a power supply device with a greater power capacity involves complicated techniques and more difficult fabrication processes. Not only fabrication cost is higher, the size and cooling also are technical bottlenecks difficult to overcome. Moreover, when in use, if all of the hardware equipment have not been fully utilized, waste of electric resource occurs.
The servers encounter another situation. As the computer has to be operated for a long period of time, if only a single large power supply device is used, in the event of malfunction or damage, the entire server has to be stopped for replacement. End users also have to stop operation.
In view of the aforesaid concerns, the higher capacity power supply device is more expensive and involves higher technical level, multi-layer power supply devices configured in a stacked or juxtaposed fashion have been developed. They may be divided into parallel power supply mode and backup power supply mode. The parallel power supply mode integrates a plurality of lower capacity power supply devices to become a higher capacity power supply system. The backup power supply mode can tolerate dysfunction or breakdown of one or more power supply devices. Hence they differ mainly in the total output power. For instance, integrating four power supply devices each having 100W capacity into a power supply system, the parallel power supply mode has total integrated power output of 400W, while the backup power supply mode may spare a portion of power (100W) and integrate and output the rest of power (300W).
Thus the parallel power supply mode can only be activated when all the power supply devices are in normal operating conditions to avoid overloading and ensure safety. Compared with the backup power supply mode, the parallel mode has an additional confirmation procedure. Hence the control circuit designs of the two modes are different. The present manufacturers have to develop and fabricate products according to two types of specifications. From user's standpoint, the server of some workstations needs the parallel mode power supply system to provide a greater power to meet loading requirements, while some servers require the backup mode power supply system that is adjustable according to different requirements. Both of them cannot be commonly shared. It creates a lot of troubles for users. To solve this problem, users often have to purchase a spared backup power supply system at an additional cost. Both look the same. Exchange and replacement take times and more efforts. It is not convenient.